Periodontal diseases are characterized by an inflammatory process in periodontal tissues caused by bacterial infection, resulting in the destruction of the periodontal soft tissue and alveolar bone. Fusobacterium nucleatum, for example, is an anaerobic Gram-negative non-sporeforming oral bacterium found in the normal flora of human mouth, that plays a major role in initiation and progression of periodontal diseases. The bacterium can adhere to a wide range of other major dental pathogen organisms, such as Porphyromonas gingivalis, and contribute to the development of periodontitis as well as invasive human infections of the head and neck, chest, lung, liver and abdomen.
Traditional approaches for reducing the bacterial load include mechanical removal and chemotherapy, the effectiveness of which is compromised by patient motivation, manual dexterity and the development of resistant species. In addition, the limited penetration of chemotherapeutic agents into bacterial biofilm results in reduced susceptibility to this kind of treatment.
Alternative approaches for reducing the bacterial load such as lethal photosensitization, using a photosensitizer in conjunction with visible light, have been suggested. Photosensitizers absorb an incident light that matches the wavelength of their peak absorption, results in killing of bacteria by a photochemical mechanism. The addition of exogenous photosensitizer to the target bacterial cells is required for lethal photosensitization. Nevertheless, some bacteria such as black-pigmented bacteroides possess endogenous porphyrins. Previous studies showed that low fluences of argon laser irradiation (wavelength, 488-514 nm) exert a phototoxic effect on Porphyromonas and Prevotella sp. Propionibacterium acnes, a Gram-positive porphyrine producing microorganism, was also inactivated by visible light without exogenous photosensitizer. Visible light (408-750 nm) was found mutagenic and caused metabolic and membrane damage of bacterial cells such as Escherichia coli, and a loss of colony-forming ability after illumination in seawater. The involvement of oxygen and reactive oxygen species (ROS) in the phototoxic effect of visible light on E. coli in seawater microcosms was shown. It has been demonstrated that ROS are also mediators of lethal photosensitization of Streptococcus mutans, in the presence of the light-activated toluidine blue O.
U.S. Pat. No. 5,611,793 to Wilson et al. discloses a method of disinfecting or sterilizing microbes infected tissues of the oral cavity by topically applying a photosensitising compound to the treated tissue and irradiating it with laser light, such as the red light helium neon gas lasers (632.8 nm) and gallium arsenide lasers (about 660 nm), at a wavelength absorbed by the photosensitising compound. A photosensitiser solution is administrated to contact with the microbes for a period of time to enable the microbes to take up some of the photosensitiser and become sensitive to the laser light. Then the laser light is introduced and the microbes are disinfected. Moreover, Wilson et al are stating in their patent that irradiation of both Gram-positive and Gram-negative oral bacteria in the absence of the photosensitisers had no detectable effect on the viability of these organisms.
U.S. Pat. No. 5,658,148 to Neuberger et al. discloses a method and a device for cleaning teeth by a low power diode laser applying the principle of photodynamic therapy. This method is based on using a photosensitizer compound. The photosensitizer compound produces singlet oxygen upon irradiation by the laser light. The singlet oxygen thus produced destroys oral bacteria.
Light is traditionally emitted in the oral cavity by various means, such as laser articulated arm, hollow fibers, fiber optics, and other tip instruments. Hence, U.S. Pat. No. 4,784,135 to Azar et al. teaches a toothbrush-like device wherein bacteria are stained preferably by applying a liquid or paste like formulation containing a bacterial selective dye within the oral cavity preferably followed by rinsing the oral cavity to wash out excess dye. The bacteria within the dental plaque are thus selectively stained by the dye and destroyed by visible light radiation.
Blue light (wavelength, about 400-500 nm) photocuring sources, such as the quartz-tungsten-halogen lamp (halogen lamp), the light emitting diode (LED) and the plasma-arc curing (PAC), are often used in dentistry for curing resin-composite materials. Non-coherent visible light kills Porphyromonas sp. presumably by a photochemical mechanism similar to that of argon laser. The toxic effect of visible light appears to be due to oxygen-dependent stimulation of ROS production.
A phototoxic effect of visible light sources mainly on the oxygen susceptible anaerobic bacteria, such as P. gingivalis and F. nucleatum, provided without utilizing any exogenous photosensitizers is hereto a long felt need.